(i) Field of the Invention
The present invention relates to a plant for liquid-phase filtration of a cryogenic fluid. It further relates to a filtration method and to a use of a filtration component for the filtration of such a cryogenic fluid in liquid phase.
The invention is applicable, in particular, in the agro-foodstuffs industrial field and in the pharmaceutical field. Since, it is necessary to guarantee perfect hygiene and asepsis of the cryogenic fluids employed the term "sterilized" cryogenic fluid is sometimes even used.
(ii) Description of Related Art
By way of illustration, when carbon dioxide (CO.sub.2) is used as a refrigerant for cooling food products, it is necessary to ensure that it is free from pathogenic microorganisms and/or particles.
Similarly, and still by way of illustration, in the pharmaceutical field when nitrous oxide (N.sub.2 O) is dispensed to a patient in a ventilator, it has to be filtered beforehand in order to ensure that the gas is sufficiently pure.
It has been found that filtration of these cryogenic fluids is difficult because of the risks of vaporization or solidification (depending on the fluid in question) resulting from use of the filtration component. For example, in the case of carbon dioxide, the problem is therefore further exacerbated by the fact that liquid carbon dioxide has a tendency to be converted into the solid state, creating "dry ice" which obstructs the ducts in the filtration plant.
It is known, in order to filter liquid nitrogen in liquid phase (and therefore recover an essentially non-diphasic fluid at the filtration outlet) to arrange the filtration component inside a bath of cryogenic liquid (in general of the same type as the one to be filtered), providing continuous cooling of the filtration component.
Such a solution for the filtration of liquid nitrogen is proposed, for example, in the document U.S. Pat. No. 4,759,848.
Although such means for cooling the filtration component are indispensable for cryogenic fluids such as nitrogen and oxygen, which have very low liquefaction temperatures, it would be advantageous, for cryogenic fluids having higher liquefaction temperatures, such as carbon dioxide or indeed nitrous oxide, to provide filtration plants which are less elaborate, albeit equally effective in terms of filtered-particle size, which do not require the utilization of cooling means and in which the filter can be kept in ambient environment and, in particular, at ambient temperature in the region of 20 or 25.degree. C.
The expression "ambient environment" means the atmospheric conditions of temperature and pressure prevailing in the room in which the filtration plant is arranged.